Fiber optics researchers have developed a simple, inexpensive technique for making optical fibers with compound glass cores. Compound glass fibers are of current interest for their high optical nonlinearity and for transmission into the infrared spectral region in applications such as Raman amplifiers, fiber lasers, and continuum generation.

The new Virginia Tech process involved melting the glass in a conventional crucible, then drawing the molten glass into a cladding tube to form a preform. After cooling, the preform can be drawn or over-cladded. The technique relies on the melting temperatures of the core glasses being less than that of the cladding tube.

Left: Preparing the tubeRight: Preform just after the suction of core glass into the silica cladding tube

“The core-suction technique eliminates several process steps compared with other techniques, which can lead to contamination,” explained Nitin Goel (Ph.D. ’05) who developed the process with his advisor Roger Stolen and others.

The core-suction technique produces little waste. Its efficiency means that more expensive, high-purity materials can be used and that organizations can easily make fibers with small quantities of different nonconventional, highly nonlinear core glasses.

The patented stub-loaded helix antenna, invented in an ECE laboratory in the 1990s, has been selected as one of 100 successful technology transfer cases in the 2006 publication of the Association of University Technology Managers. Warren Stutzman and graduate student Mike Barts developed the antenna, which is used around the world for wireless internet connections. The antenna is valued for its use in difficult applications where long distances or building penetration is needed, such as cities and hotels. FRC Corp. in Mason City, Iowa, is the exclusive licensee of the antennas and claims they are considered the best performing 2.5 GHz range antennas in the field today. The firm says sales are growing and they are geared up to produce 1 million antennas a year.

ECE researchers in the Center for Photonics Technology claim to be the first to prove experimentally that the speed of light is independent of the time the light has traveled.

Anbo Wang, with graduate students Bo Dong and Ming Han, used an active Mach-Zehnder interferometer illuminated by sunlight. They measured the difference in optical fibers between the speeds of light from a star (the sun) and the stimulated emission from an optical amplifier as presented by the interferomter.

The speed difference of the stimulated emission and sunlight was obtained by measuring the phase change when the interferometric signal propagates along a span of a single-mode fiber. The test measured a constant speed with an accuracy of 1.6x10-11/year.

“The speed of light as a universal constant must be tested with ever-increasing accuracy as our applications get more sophisticated and the interpretation of the constancy of light speed is manifold,” Wang said. In the past century, experiments have tested that the speed of light is independent of the motion of the observer and independent of light frequency. Recently another postulate that the speed does not vary with time and space, has drawn a great deal of attention as experiments may suggest possible variations of the fine structure constant with time, according to Wang. “However, to our best knowledge, there has been no experimental test on the constancy of light speed with respect to photon age, even though it has been universally accepted,” he said.